The yeast Saccharomyces cerevisiae serves as a model eukaryote to study the regulation of membrane phospholipid synthesis. The genes and enzymes in the phospholipid synthesis pathways are regulated by genetic (e.g., zinc depletion) and biochemical (e.g., phosphorylation) mechanisms. Recent studies have shown that phospholipid synthesis is regulated by the stress condition of zinc depletion. Zinc is an essential element required for the optimal growth and metabolism of eukaryotic cells. Preliminary data indicated that a pathway for synthesizing phosphatidylcholine, the most abundant membrane phospholipid, was activated to allow cells to deal with this stress. In this application, I will examine the regulation of CK/7-encoded choline kinase, the enzyme that catalyzes the committed in the Kennedy pathway, in response to zinc depletion. I will measure the levels of choline kinase activity, protein, and mRNA. Transcription of the CKI1 gene will be monitored using a Pc/c/r/acZ reporter gene. Identification of the promoter element(s) and transcription factor(s) involved will be pursued. The phosphorylation state of choline kinase in response to zinc depletion will be monitored by in vivo labeling of the protein with 32P, using wild type and available phosphorylation site mutants.